1. Field of the Invention
This invention generally relates to blends of poly(ester amide) (PEA) polymers or copolymers with a low glass transition temperature (Tg) and PEA polymers or copolymers with a high Tg, which are useful for coating an implantable device such as a drug-delivery stent.
2. Description of the Background
Poly(ester amide) polymers are known for their relatively low glass transition temperatures. For example, co-poly-{[N,N′-sebacoyl-bis-(L-leucine)-1,6-hexylene diester]-[N,N′-sebacoyl-L-lysine benzyl ester]} (PEA-Bz) and co-poly{[N,N′-sebacoyl-bis-(L-leucine)-1,6-hexylene, diester]-[N,N′-sebacoyl-L-lysine 2,2,6,6-tetramethyl-4-amino-1-piperidinyloxyl amide]} (PEA-TEMPO) have a Tg of approximately 23° C. and 33° C., respectively.
Complications related to low Tg manifest themselves as reduced drug release rate control, increased polymer degradation rate, reduced shelf life stability, and potentially increased system mechanical failures. Low Tg materials usually have higher drug permeabilities, which necessitates the use of greater amounts of polymer to control release rate of the drug. Moreover, the low Tg enables the drug to diffuse within the coating. In other words, the drug distribution within a given coating can change with time until an equilibrium state is reached, resulting in release rate shifts. Low Tg materials also tend to be softer, they can be more adhesive to balloons, and are more prone to failure during mechanical perturbations such as crimping and expansion.
The embodiments of the present invention provide for methods addressing these issues.